ATTN: Mechanics... Shimano Taper-Fit Crank Arm Problem



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H

Hkek

Guest
1999 Shimano LX cranks with UN72 Bottom Bracket:

What is wrong with this picture?

I have been trying to chase down a squeaking noise. After disassembling and inspecting the cranks
arms I have discovered that the crank arm on the drive side, when fully tightened, slides onto the
square taper BB such that it "bottoms out" against a shoulder on the BB.

There is no such shoulder on the non-drive (left) side, so the fit of the left crack is truly
determined by the taper. On the drive (right) side, however, the crank arm contacts the shoulder,
which therefore defeats the purpose of the taper.

How common is this condition?

I will openly admit that I have removed the cranks several times over the years and have always
applied high-pressure (marine) wheel bearing grease to the tapers prior to assembly. I now see that
Barnett's Manual emphatically states not to use grease on taper-fit cranks.

Have I stretched and deformed the taper in the crank arm, or might they have "come from the factory"
with a poor fit?

Should I attempt to correct the fit by removing some material from the crank arm to provide some
clearance (prevent bottoming out) between the crank arm and BB shoulder?

Thanks in advance for sharing your experience/knowledge on the subject!
 
Q

Qui Si Parla Ca

Guest
coolmale-<< when fully tightened, slides onto the square taper BB such that it "bottoms out" against
a shoulder on the BB.

<< I now see that Barnett's Manual emphatically states not to use grease on taper-fit cranks.
>><BR><BR>

<< Have I stretched and deformed the taper in the crank arm, or might they have "come from the
factory" with a poor fit?

Number one...new crank time.

Peter Chisholm Vecchio's Bicicletteria 1833 Pearl St. Boulder, CO, 80302
(303)440-3535 http://www.vecchios.com "Ruote convenzionali costruite eccezionalmente bene"
 
M

Mark Hickey

Guest
[email protected] (HKEK) wrote:

>How common is this condition?

Fairly common to those who have their cranks on and off a lot.

>I will openly admit that I have removed the cranks several times over the years and have always
>applied high-pressure (marine) wheel bearing grease to the tapers prior to assembly. I now see that
>Barnett's Manual emphatically states not to use grease on taper-fit cranks.

That's a religious issue. Fact is, dry or greased, putting on a crank arm with the proper torque on
the bolt will result in a very reliable interface that won't fail.

>Have I stretched and deformed the taper in the crank arm, or might they have "come from the
>factory" with a poor fit?

You did it with the multiple installations (and possibly excessive torque?).

>Should I attempt to correct the fit by removing some material from the crank arm to provide some
>clearance (prevent bottoming out) between the crank arm and BB shoulder?

Nope. It's time for a new crank.

Mark Hickey Habanero Cycles http://www.habcycles.com Home of the $695 ti frame
 
C

Chris B .

Guest
On 9 Jun 2003 06:07:09 -0700, [email protected] (HKEK) wrote:

>1999 Shimano LX cranks with UN72 Bottom Bracket:
>
>What is wrong with this picture?
>
>I have been trying to chase down a squeaking noise. After disassembling and inspecting the cranks
>arms I have discovered that the crank arm on the drive side, when fully tightened, slides onto the
>square taper BB such that it "bottoms out" against a shoulder on the BB.

If there is noise while everything is clean and torqued properly (grease or no grease) then there is
probably damage to the crank.

>There is no such shoulder on the non-drive (left) side, so the fit of the left crack is truly
>determined by the taper. On the drive (right) side, however, the crank arm contacts the shoulder,
>which therefore defeats the purpose of the taper.
>
>How common is this condition?

Probably not that common since most people leave the cranks alone for a long time once they are
installed. Any crank will wear out this way given enough repeated installations and removals (you
don't say exactly how many). Every time you install them, even with grease, a bit of material is
going to be displaced. Since it sounds like you have taken them on many times and you apparently are
using a Shimano BB with a non-removeable ring around the spindle for the right crank to seat against
(unless I misunderstand), it is not surprising that you no longer get a tight fit.

>I will openly admit that I have removed the cranks several times over the years and have always
>applied high-pressure (marine) wheel bearing grease to the tapers prior to assembly. I now see that
>Barnett's Manual emphatically states not to use grease on taper-fit cranks.

As Mark H. points out, this is a religious issue but it doesn't seem to matter too much in practice.
More important is to torque the crank bolts sufficiently.

Another possibility is that you are in the habit of re-tightening the cranks some time after initial
installation. This will drive the crank further up the taper when you ride them hard again, though
the problem whould have shown up quickly and usually it's the left side which shows problems first

>Have I stretched and deformed the taper in the crank arm, or might they have "come from the
>factory" with a poor fit?

Riding the cranks loose (which is what you are doing now, by the sounds of it) is what quickly
deforms the hole. Riding after continually re-tightening will do damage more gradually while
repeated installations will be more gradual still.

>Should I attempt to correct the fit by removing some material from the crank arm to provide some
>clearance (prevent bottoming out) between the crank arm and BB shoulder?

I wouldn't bother, it sounds like the crank taper is shot anyhow and you don't really want to be
removing material or overtightening things down there anyway. If you are going to continue to need
to take the cranks on and off often, you might consider a splined interface next time; in theory,
one that uses pinch bolts for the preload would be a good bet.

>Thanks in advance for sharing your experience/knowledge on the subject!

You're welcome.

Chris Bird
 
P

Peter Headland

Guest
Whatever you did, it was nothing to do with greasing the spindle.
 
M

Mark Hickey

Guest
"Stan Cox" <[email protected]> wrote:

>
>"Mark Hickey" <[email protected]> wrote in message
>news:[email protected]...
>> [email protected] (HKEK) wrote:
>>
><snip
>> That's a religious issue. Fact is, dry or greased, putting on a crank arm with the proper torque
>> on the bolt will result in a very reliable interface that won't fail.
>>
>> <snip> Mark Hickey
>
>Good Grief. I havent heard anything on the net described as "a religious issue" for about 5 years.
>Reminds me of the old days....gets all nostalgic....sobs into beer....

Heathen!

Mark Hickey Habanero Cycles http://www.habcycles.com Home of the $695 ti frame
 
M

Matt O'Toole

Guest
"Mark Hickey" <[email protected]> wrote in message
news:[email protected]...

> That's a religious issue. Fact is, dry or greased, putting on a crank arm with the proper torque
> on the bolt will result in a very reliable interface that won't fail.

This is one place where a torque wrench is a good idea, unless you know you have a really good
feel for it.

Matt O.
 
D

David

Guest
"HKEK" <[email protected]> wrote in message
news:[email protected]...
> 1999 Shimano LX cranks with UN72 Bottom Bracket:
...
> Have I stretched and deformed the taper in the crank arm,

Sounds like it. When you replace 'em, if you decide to switch from square-taper cranks altogether, I
think ISIS splined is the best BB/crank interface I've used.

I got a pretty good deal on ISIS cranks + BB. Lots of similar deals around.

David
 
P

Peter Cole

Guest
"HKEK" <[email protected]> wrote in message
news:[email protected]...
> 1999 Shimano LX cranks with UN72 Bottom Bracket:
>
> What is wrong with this picture?
>
> I have been trying to chase down a squeaking noise. After disassembling and inspecting the cranks
> arms I have discovered that the crank arm on the drive side, when fully tightened, slides onto the
> square taper BB such that it "bottoms out" against a shoulder on the BB.
>
> There is no such shoulder on the non-drive (left) side, so the fit of the left crack is truly
> determined by the taper. On the drive (right) side, however, the crank arm contacts the shoulder,
> which therefore defeats the purpose of the taper.
>
> How common is this condition?
>
> I will openly admit that I have removed the cranks several times over the years and have always
> applied high-pressure (marine) wheel bearing grease to the tapers prior to assembly. I now see
> that Barnett's Manual emphatically states not to use grease on taper-fit cranks.
>
> Have I stretched and deformed the taper in the crank arm, or might they have "come from the
> factory" with a poor fit?
>
> Should I attempt to correct the fit by removing some material from the crank arm to provide some
> clearance (prevent bottoming out) between the crank arm and BB shoulder?
>
> Thanks in advance for sharing your experience/knowledge on the subject!

From the faq:

"The argument that the greased spindle will enlarge the hole of the crank and ultimately reduce
chainwheel clearance is also specious, because the crank does not operate in the plastic stress
level. At the elastic limit it would break at the attachment knuckle in a short time from metal
fatigue, that occurs rapidly at the yield stress. In fact, the depth of engagement (hole
enlargement) can increase with an unlubricated fit faster than with a lubricated one, because
installation friction is the only mechanism that reams the hole."

Is your BB centered in the BB shell? It may have had bare clearance to start with. BBs come in a
range of lengths, and are not very expensive. I'd try installing one with a slightly longer axle
rather than removing material from the crank.
 
B

Bluto

Guest
Mark Hickey <[email protected]> wrote:

> Fact is, dry or greased, putting on a crank arm with the proper torque on the bolt will result in
> a very reliable interface that won't fail.

The *interface* won't fail... only the crank spindle.

The square-taper spindle is a component proven to have zero to negative safety margin for my use;
therefore I believe it's fair to say its safety margin is inadequate for many riders.

IMO the debate about greased vs. dry tapers is like quibbling over what polish to use on your own
Sword of Damocles. Lubed or dry, pinch-bolt cranks are a better idea by far.

Chalo Colina
 
P

Phil Lee

Guest
> I wouldn't bother, it sounds like the crank taper is shot anyhow and you don't really want to be
> removing material or overtightening things down there anyway. If you are going to continue to need
> to take the cranks on and off often, you might consider a splined interface next time; in theory,
> one that uses pinch bolts for the preload would be a good bet.

I was under the impression that when you first install the cranks, they go on with pretty big
bolt torque.

The subsequent times you put them on, you tighten just enough to get it snug, but not "tight." This
would ensure a good interface between the crank/spindle faces that wouldn't move, but at the same
time wouldn't enlarge the taper hole.

Am I sorta right?

--
Phil, Squid-in-Training
 
J

Jobst Brandt

Guest
Phil Lee writes:

> I was under the impression that when you first install the cranks, they go on with pretty big
> bolt torque.

Why should there be any difference whether it is the first or any other installation? What Is it
that you perceive changing after the first installation?

> The subsequent times you put them on, you tighten just enough to get it snug, but not "tight."
> This would ensure a good interface between the crank/spindle faces that wouldn't move, but at the
> same time wouldn't enlarge the taper hole.

This press fit is far below the yield stress, the stress at which plastic deformation occurs, and
coincidentally also the stress at which fatigue failure would occur with relatively few stress
cycles (pedal strokes).

> Am I sorta right?

This is not the way scientific presentations should go. You don't just blather away as long as no
one disagrees with your hypothesis. The intent in this forum is to offer information that you know
to be correct. I suppose you belong to those who believe there are no facts, only opinions and
their truth depends on how many people repeat them. Chicken little thought that too but the sky
did not fall.

Jobst Brandt [email protected] Palo Alto CA
 
C

Chris B .

Guest
On Wed, 11 Jun 2003 04:25:02 GMT, "Phil Lee" <[email protected]> wrote:

I wrote:

>> I wouldn't bother, it sounds like the crank taper is shot anyhow and you don't really want to be
>> removing material or overtightening things down there anyway. If you are going to continue to
>> need to take the cranks on and off often, you might consider a splined interface next time; in
>> theory, one that uses pinch bolts for the preload would be a good bet.

>I was under the impression that when you first install the cranks, they go on with pretty big
>bolt torque.
>
>The subsequent times you put them on, you tighten just enough to get it snug, but not "tight." This
>would ensure a good interface between the crank/spindle faces that wouldn't move, but at the same
>time wouldn't enlarge the taper hole.
>
>Am I sorta right?

I'm not sure I follow you; putting aside any wear and tear to the crank taper, I think you need to
ensure that the crank is tight enough every time so that it doesn't move on the spindle when you
pedal hard. You are only stretching the crank in the elastic sense when you press it on so as to
preload it but I don't think you are permanently enlarging the hole (except that in practice, a
little material is going to be removed which any well used crank will show). It's the movement that
happens when you ride the crank loose that rounds out the hole.

So to that end, I suggested that he not compensate for wear and tear by overtightening because the
interface is already under a lot of stress and this may cause the crank to split. I recently had
this happen about a week after I foolishly wrenched down hard on a crank which had suddenly loosened
after having stayed tight for about a year (this is my beater bike and the crank was imperfect when
I installed
it). It happened right in the middle of an intersection while doing a left turn - very embarassing!
No damage other than the crank but it's not an experience I would want to repeat myself, nor have
others repeat.

Chris Bird
 
S

Shaun Rimmer

Guest
<[email protected]> wrote in message news:yhzFa.1517$%[email protected]...
> Phil Lee writes:
>
> > I was under the impression that when you first install the cranks, they go on with pretty big
> > bolt torque.
>
> Why should there be any difference whether it is the first or any other installation? What Is it
> that you perceive changing after the first installation?
>
> > The subsequent times you put them on, you tighten just enough to get it snug, but not "tight."
> > This would ensure a good interface between the crank/spindle faces that wouldn't move, but at
> > the same time wouldn't enlarge the taper hole.
>
> This press fit is far below the yield stress, the stress at which plastic deformation occurs, and
> coincidentally also the stress at which fatigue failure would occur with relatively few stress
> cycles (pedal strokes).
>
> > Am I sorta right?
>
> This is not the way scientific presentations should go. You don't just blather away as long as no
> one disagrees with your hypothesis. The intent in this forum is to offer information that you know
> to be correct. I suppose you belong to those who believe there are no facts, only opinions and
> their truth depends on how many people repeat them. Chicken little thought that too but the sky
> did not fall.

I have heard it said before Jobst, that you are far above yourself, and that your attitude is
atrocious, but until now, I had never seen this myself.

Phil posted that he 'was under the impression' - he did not state he was right, nor did he even
allude to it. He then followed on asking for clarification "Am I sorta right?". So, why did you
offer him bad attitude, along with the 'information that you know to be correct'?

Surely, this group exists for people who have questions, or who need clarification of myth, as well
as for people like you to parade their delicate but over-sized egos around.

Thanks for listening.

Shaun aRe - Scientific - schmientific.
 
P

Peter Cole

Guest
"Chris B." <[email protected]> wrote in message news:[email protected]...
>
> So to that end, I suggested that he not compensate for wear and tear by overtightening because the
> interface is already under a lot of stress and this may cause the crank to split. I recently had
> this happen about a week after I foolishly wrenched down hard on a crank which had suddenly
> loosened after having stayed tight for about a year

It might have loosened because it was cracking, did you inspect it carefully before you
tightened it?
 
C

Chris B .

Guest
On Wed, 11 Jun 2003 16:09:43 GMT, "Peter Cole" <[email protected]> wrote:

>"Chris B." <[email protected]> wrote in message news:[email protected]...
>>
>> So to that end, I suggested that he not compensate for wear and tear by overtightening because
>> the interface is already under a lot of stress and this may cause the crank to split. I recently
>> had this happen about a week after I foolishly wrenched down hard on a crank which had suddenly
>> loosened after having stayed tight for about a year
>
>It might have loosened because it was cracking, did you inspect it carefully before you
>tightened it?

No, I didn't.

Chris Bird
 
J

Jay Beattie

Guest
<[email protected]> wrote in message news:yhzFa.1517$%[email protected]...
> Phil Lee writes:

<snipped hypotheses regarding crank/spindle interface>

> This is not the way scientific presentations should go. You don't just blather away as long as no
> one disagrees with your hypothesis. The intent in this forum is to offer information that you know
> to be correct. I suppose you belong to those who believe there are no facts, only opinions and
> their truth depends on how many people repeat them. Chicken little thought that too but the sky
> did not fall.

Certainly the sky did not fall, but Chicken Little got hit pretty hard on the head with an out-sized
acorn. He may have misinterpreted what was happening, but his concern probably saved Henny Penny,
Cocky Locky and Goosey Poosey from serious closed head injury! But for that near mishap with Foxy
Woxy, Chicken Little would have been a hero. I figure it is the same way with bicycle cranks, minus
the fox. Isn't it? -- Jay Beattie.
 
P

Phil Lee

Guest
<[email protected]> wrote in message news:yhzFa.1517$%[email protected]...
> Phil Lee writes:
>
> > I was under the impression that when you first install the cranks, they go on with pretty big
> > bolt torque.
>
> Why should there be any difference whether it is the first or any other installation? What Is it
> that you perceive changing after the first installation?
>
> > The subsequent times you put them on, you tighten just enough to get it snug, but not "tight."
> > This would ensure a good interface between the crank/spindle faces that wouldn't move, but at
> > the same time wouldn't enlarge the taper hole.
>
> This press fit is far below the yield stress, the stress at which plastic deformation occurs, and
> coincidentally also the stress at which fatigue failure would occur with relatively few stress
> cycles (pedal strokes).

Well, then, that's great. So I shouldn't need to worry about overtightening (within reason)?

> > Am I sorta right?
>
> This is not the way scientific presentations should go. You don't just blather away as long as no
> one disagrees with your hypothesis. The intent in this forum is to offer information that you know
> to be correct. I suppose you belong to those who believe there are no facts, only opinions and
> their truth depends on how many people repeat them. Chicken little thought that too but the sky
> did not fall.

It wasn't a presentation of my original thinking. It wasn't my hypothesis; it was something that
I though originated from this NG a few months ago. Why must you categorize me as a chicken
little person?

Maybe we should all keep our hypotheses to ourselves. That will get us far. Thanks for you
input anyway.

--
Phil, Squid-in-Training
 
D

Dave Kahn

Guest
"Shaun Rimmer" <[email protected]> wrote in message
news:<[email protected]>...
> <[email protected]> wrote in message news:yhzFa.1517$%[email protected]...

> > This is not the way scientific presentations should go. You don't just blather away as long as
> > no one disagrees with your hypothesis. The intent in this forum is to offer information that you
> > know to be correct.

> Phil posted that he 'was under the impression' - he did not state he was right, nor did he even
> allude to it. He then followed on asking for clarification "Am I sorta right?". So, why did you
> offer him bad attitude, along with the 'information that you know to be correct'?

Because he was sorta vague about a sorta procedure that was sorta wrong. I presume Phil is sorta
grown up and can sorta look after himself. Sorta.

--
Dave...
 
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